Low pressure accumulators are commonly used in anti-lock brake systems to accommodate a volume of fluid released by a wheel brake apply piston during anti-lock brake actuation when a fluid pump is not pumping fluid. A piston within the low pressure accumulator is displaced with relative ease by the pressurized fluid from the brake piston, enabling release of the brake. When it is displaced by pressurized fluid, the piston compresses the accumulator spring and displaces air from a spring side of the accumulator chamber. When the pump is cycled on, fluid is drawn from the low pressure accumulator, allowing the piston to return to its original position. The piston is biased to a zero volume position by an accumulator spring. Air is drawn back into the spring side of the accumulator chamber.
The spring side of the chamber is commonly vented by providing a cover over an end of the accumulator spring chamber which has a one way lip seal around a periphery of the cover which seals against an inner wall of the accumulator chamber. The one way lip seal deflects to enable air to flow past it and out of the chamber when pressure inside the chamber exceeds atmospheric pressure, but seals against the chamber wall to prevent air or any other fluid from entering when pressure inside the chamber is less than atmospheric pressure. One potential side effect of the inability of the lip seal to allow air to return to the spring chamber is that it will slow or prevent the return of the piston when the pressurizing pump is activated. If the piston cannot return to a zero volume position, its capacity may be compromised to the point that it may not be possible to achieve a full release of the wheel brake during anti-lock brake cycling actuation. However, if air can re-enter the chamber without any type of restriction, then water and other contaminants may induce corrosion and interfere with the movement of the piston. Such interference would also result in a compromising of the capacity of the accumulator. It is therefore necessary that any means for enabling the return of air to the accumulator chamber prevent the entry of water and other contaminants which can cause the piston to corrode and/or stick in the accumulator chamber.
It is desired to provide a cover for a low pressure accumulator which allows air to move in and out of the accumulator chamber freely while blocking water and other contaminants from entering the accumulator chamber.